The present invention relates to a method of manufacturing fillings or paddings, designed in particular for the seats of motor vehicles.
Such fillings generally consists of two or more layers of foam having different flexibility characteristics in order to ensure that passengers using the seats containing this filling are comfortable.
Methods of manufacturing fillings are known, in particular from FR-A-2 607 061, which consist in injecting several foams of different flexibility into a mould in succession. The foams are injected one after the other without being separated. This method has a disadvantage in that it is difficult to control the distribution of the foam layers in the mould with the result that a filling is obtained in which the different parts are of a flexibility that is not adapted to passenger comfort.
Document FR-A-2 722 726 also discloses a method of manufacturing fillings in which foams of different flexibility are successively injected into a mould, these foams being separated by an articulated element. However, although this method is entirely satisfactory as regards producing a filling that is comfortable for the passenger, it is expensive and the foam is at risk from tearing during the moulding process.
The objective of the present invention is to overcome the above-mentioned disadvantages by proposing a method of manufacturing a filling which has several layers of foam of differing flexibility in a single moulding process, without the need for an insert, whilst controlling the distribution of the foam and, in doing so, producing a very good finish.
To this end, the invention proposes a method of manufacturing a filling by introducing at least two layers of polyurethane foam into a mould, the filling comprising at least one bearing face and one supporting face opposing the bearing face and the mould having a base and a cover which match the shapes of the faces of said filling, the method comprising steps which consist in:
introducing a first flexible foam compound at least into a central part of the base of the mould;
allowing the first foam compound to expand naturally so as to form a skin in contact with the air; and
introducing a second flexible foam compound in direct contact with the skin formed by the first foam compound and closing the mould; and
allowing the second foam compound to expand so that the foam occupies the entire volume of the mould, and being essentially characterised in that this step by which the first foam compound is introduced consists of a spraying process and the step by which the second foam compound is introduced consists of an injection process.
The manufacturing method proposed by the invention may optionally also incorporate one or several of the following features:
the quantity of the first foam compound injected is such that after the expansion step, the skin obtained is substantially smaller in thickness than the overall thickness of the filling and is between approximately 0.5 and 50 mm;
the spraying step consists in spraying a mixture of isocyanate and polyol formulated at a pressure of between 60 and 250 bar and at a temperature ranging between 200xc2x0 C. and 100xc2x0 C.;
the formulated polyol comprises a mixture of water varying from 1 to 5 parts, gel catalyst varying from 0 to 4 parts, gas catalyst varying from 0 to 4 parts, cell opener varying from 0 to 5 parts and stabiliser varying from 0 to 2 parts; and
prior to the step at which the first foam compound is introduced into the mould, a finishing cover is placed in the base of the mould.
Another objective of the invention is a filling produced by the above-mentioned method, in which the skin formed by the first foam compound is of a thickness substantially smaller than the overall thickness of the filling.
By preference, the hardness of the skin is between 1 and 12 kPa and the hardness of the layer corresponding to the second foam compound is between 2 and 15 kPa.
Even more preferably, the flexibility of the second foam compound is lower than the flexibility of the first foam compound.
Another objective of the present invention is to provide a seat comprising such a filling.